Because of advances in methods for neuroimaging and genetic linkage, we now have the means to make important gains in our knowledge of the biological mechanisms and etiologies of autism. Advances depend, in part on more precise and specific definitions of the language phenotypes of autism, particularly in their family members who often have traits that are conceptually similar to components of the core disorder. The goals of this proposed study are to characterize more precisely the language phenotype found in the first degree relatives (parents and siblings) of autistic probands, to assess its specificity by similarly assessing families identified through a proband with specific language Impairment (SLI) and to explore the relationship between the language phenotype in probands (both autism and SLI) and their family members. We hypothesize that the autistic probands and their families will have abnormalities mainly in pragmatic and discourse aspects of language while the SLI families will have predominantly structural language deficits particularly in syntax/morphology and phonology/fluency. We also hypothesize that there will be some overlap between these populations which may reflect commonalities in etiology or mechanism of the two disorders. In this collaborative effort between the Eunice Kennedy Shriver Center and the University of Iowa, we propose to study the probands and first degree relatives of 100 families with a child with SLI, and 50 normal control families. All probands and their parents and siblings will be given parallel measures of intelligence, reading, spelling and language including standardized test, experimental procedures and natural language samples to quantify both pragmatic and structural aspects of language.